Food Chemistry

15.4 Baked Products 723

leavening is achieved by a sour dough formula-
tion which includes lactic and acetic acid bacteria.

15.4.1.6.1 Yeast

A given amount (Table 15.48) of surface-
fermenting yeast,Saccharomyces cerevisiae,is
used. While normal yeasts preferentially degrade
sucrose rather than maltose, special rapidly
fermenting yeasts are used which metabolize
both disaccharides at the same rate, shortening
the fermentation time.
Yeasts differ in their growth temperature optima
(24–26◦C) and their fermentation temperature
optima (28–32◦C). The optimum pH for growth
is 4.0–5.0. In addition to CO 2 and ethanol, which
raise the dough, the yeast forms a variety of
aroma compounds (cf. 5.3.2.1). Whether other
compounds released by the growth of yeast
would affect the dough rheology is unclear; there
appears to be no effect of yeast proteinase and
GSH.

15.4.1.6.2 Chemical Leavening Agents

The interaction of water, acid, heat and chemical
leavening agents (baking powders) releases CO 2.
The release of gas may occur in the dough prior
to or during oven baking. The agents consist of
aCO 2 -generating source, as a rule sodium bicar-
bonate, and an acid carrier, usually disodium di-
hydrogendiphosphate, sometimes monocalcium
phosphate[Ca(H 2 PO 4 ) 2 ]. Glucono-δ-lactone or
tartar (acidic potassium tartrate) are used as acid

Table 15.48.Amount of yeast used in bread and other
baked products

Baked product Yeast addeda
(%)

Rye bread 0 .5–1. 5
Rye mix bread 1 .0–2. 0
Wheat mix bread 1 .5–2. 5
Wheat bread 2 .0–4. 0
Breakfast rolls 4 .0–6. 0
Rusk (“Zwieback”) 6.0–10. 0

aBased on flour content.

carrier for phosphate-free baking powder. The

phosphate-free leavening mixtures produced on

an industrial scale contain citric acid or its acidic

sodium salt. In baking powder, the two reactive

constituents are blended with a filler which

consists of corn, rice, wheat or tapioca starch or

sometimes dried wheat flour. The filler content in

the powder is up to 30%. The role of the filler is

to prevent premature release of CO 2 .Themarket

also offers baking powders flavored with vanillin

or ethyl vanillin.

For every 500 g of flour, baking powder should

develop 2.35–2.85 gCO 2 , equivalent to about

1 .25 liters.

In individual cases, NaHCO 3 alone is used for

some flat shelf-stable cookies and ammonium

hydrogencarbonate (NH 4 HCO 3 ) for many

others. Ginger and honey cookies are leavened

by NH 4 HCO 3 , mostly together with potash

(K 2 CO 3 ). To a small extent, a 1:1 mixture of

ammonium hydrogencarbonate and ammonium

carbamate (H 2 NCOONH 4 ) is used in some coun-

tries. Both decompose above 60◦CtoNH 3 ,CO 2

and water.

15.4.2 Dough Preparation

15.4.2.1 Addition of Yeast to Wheat Dough

15.4.2.1.1 Direct Addition

Flour, water, yeast, salt and other ingredients are

directly mixed into the dough.

15.4.2.1.2 Indirect Addition

Yeast is propagated at 25–27◦C in a well-aerated

liquid pre-ferment which contains flour, water

and some sugar. After a given time, the liquid

is blended with the bulk of flour and water and

other ingredients and then made into a dough in

amixer.

For continuous indirect addition of yeast, special

liquid starters (sponges) with a pH of 5.0–5. 3

are also used with incubation at 38◦Ctodevelop

aroma. Such matured fermented sponge is then

metered continuously into a kneader which han-

dles the dough.